Wave-power electric device and method

ABSTRACT

The present invention relates to a wave-power unit having a floating body ( 3 ) and a rotating electric generator ( 5 ) mechanically connected to the floating body ( 3 ). In accordance with the invention a mechanically movement transmitting means ( 4 ) is arranged for transmission of vertical movements of the floating body ( 3 ) to rotary movements of the generator rotor. The invention also relates to a wave-power plant composed of a number of wave-power units in accordance with the invention. The invention also relates to the use of the claimed wave-power unit and method of generating electric energy.

BACKGROUND OF THE INVENTION

1. Technical Field

A first aspect of the present invention relates to a wave-power unit forthe production of electric power, comprising a floating body and arotating electric generator connected to the floating body.

A second aspect of the invention relates to a wave-power plantcomprising a plurality of wave-power units in accordance with theinvention.

A third aspect of the invention relates to the use of the claimedwave-power unit for producing electric current.

A fourth aspect of the invention, finally relates to a method ofgenerating electric power by mechanically connecting a floating body toan electric generator.

The wave-power unit in accordance with the invention is primarilyintended for, but not limited to, applications up to 500 kW.

2. Background Art

Wave movement in the sea and in large inland lakes constitutes apotential source of energy that has scarcely been exploited so far. Theavailable wave energy is dependent on the height of the waves, andnaturally differs in different locations. The average wave energy duringa year is dependent on the various wind conditions, which are greatlyinfluenced by the distance of the location from the nearest coast.Measurements have been carried out in the North Sea, for instance. Atone measuring point approximately 100 km west of the coast of Jylland,Denmark, where the depth was about 50 m, wave heights were measured overa long period of time and the available energy was calculated. Thefollowing table was obtained:

Wave period Output Height of wave m sec. kW/m Hours/Year <0.5 — — 966 14 2 4103 2 5 12 1982 3 6 32 944 4 7 66 445 5 8 115 211 >5.5 >145 119

Thus, during slightly less than half the time the height of the waves isabout 1 m, producing an output of 2 kW/m. However, the most energy isavailable from wave heights in the region of 2–5 meter, taking intoconsideration that the output increases greatly with increased waveheight.

Various types of wave-power units have been proposed to utilize theenergy available from the wave movement in the ocean for generatingelectric power. However, these have been unsuccessful in competing withconventional production of electric power. Wave-power plants realized sofar have been primarily experimental plants or have been used to supplypower locally for navigation buoys. If commercial production ofelectricity is to be possible, thus providing access to the vast reserveof energy in the movement of ocean waves, is it not only necessary toplace the units in suitable spots, it is also necessary for the unit tobe reliable in operation, highly efficient and low in manufacturing andrunning costs.

Many of the known devices for generating electric power from wave energyare based on principles according to which water is pumped or aircompressed in order to drive a generator turbine. Several links are thusinvolved in the energy conversion process, which affects the totalefficiency negatively. Such units are also complicated, and thusexpensive.

It is also already known to use an electric linear generator which isdirectly connected to a floating body. This avoids many of the drawbacksmentioned above.

From certain aspects, however, a rotating generator offers advantagesover a linear generator.

Besides the above-mentioned types of units with generators driven byturbines it is also already known to directly transmit the wavemovements to a rotating electric generator. However, this is only forsupplying energy locally and the output is relatively little. Thus, alight buoy is known through U.S. Pat. No. 5,176,552 that is suppliedwith energy from the movement of the buoy in the waves. A rotatingelectric generator is thus arranged inside the light buoy. The rotor ofthe generator is connected by a cable with a substantially stationaryplate located deep down in the water. When the buoy is moved up and downby the waves, the cable causes the rotor to rotate. For several reasonsthis device is not very suitable for producing electric power to supplyan electric supply network of a financially interesting size.

The object of the present invention is, in the light of the above, toproduce a wave-power unit of the relevant type which fulfils the demandsfor high efficiency, reliable operation and cost effectiveness, andenables the generation of electric power for supply to an electricsupply network.

SUMMARY OF THE INVENTION

The objective set has been achieved in accordance with the first aspectof the invention in that the wave-power unit comprises the specialfeature that a mechanical movement transmitting means is arranged totransmit vertical movements of the floating body to rotary movements ofthe rotor.

Thanks to the movement transmitting means a rotary movement is obtainedwhich enables the use of a rotating electric generator. The rotarymovement is normally oscillating since the linear movement is to andfro.

The unit in accordance with the invention thus enables the advantages ofa rotating electric generator to be exploited without the intermediateenergy conversion steps required by known applications, and this in sucha manner that generation of electric power on a larger scale isfinancially practicable.

In accordance with a preferred embodiment of the claimed wave-power unitat least the stator of the generator is enclosed in a housing anchoredin the sea/lake bed.

Enclosing the generator or only its stator in a watertight housing meansthat it is protected from attack by the surrounding salt water or theinfluence of living organisms in the water such as acorn barnacles. Italso enables the use of a relatively simple generator of standard type.Anchoring the generator in the sea bed via the housing fixes theposition of the generator in relation to the floating body and enablesoptimal utilization of the vertical movements of the floating body.

In accordance with another preferred embodiment the rotor is alsoenclosed in the housing.

The whole generator is thus protected from corrosion and the advantagesof the enclosure are thus exploited to a greater extent.

In accordance with yet another preferred embodiment the rotor issituated on the outside of the stator.

Although a conventional placing with the rotor inside the stator is inmost cases preferable, in certain cases the embodiment with the statoroutside enables simpler transmission of the linear movement of thefloating body to rotary movement of the rotor.

In accordance with another preferred embodiment the rotor is connectedto a turning body, which turning body is connected to the movementtransmitting means.

The turning body enables efficient conversion of the linear movement torotary movement to be achieved in a very simple way and allowsconsiderable freedom of design to achieve this. It also createsexcellent opportunity for achieving an optimal movement pattern of therotor.

In accordance with yet another preferred embodiment the turning body isarranged outside the housing.

The lead-in through the housing for transmitting the movement willtherefore be advantageous from the sealing point of view since in thisembodiment it can be designed as a lead-in for a rotating, but otherwisestationary, shaft. This entails least sealing problems.

In accordance with still another preferred embodiment the unit comprisesa first gear mechanism effecting a gear change between the movements ofthe turning body and the rotor.

Thanks to the gear mechanism the peripheral speed of the rotor can beincreased so that the frequency of the induced voltage is increased.This is advantageous since the speed of the linear movement isrelatively slight.

In accordance with a further embodiment of the claimed wave-power unitthe movement transmitting means is secured by its upper end to thefloating body and by its lower end to the turning body so that at leastthe lower part of the movement transmitting means consists of acomponent that can be rolled up, e.g. a cable.

In such an embodiment the conversion from linear movement in thefloating body to rotary movement in the turning body takes place in astructurally simple manner and with slight losses. At the same time sucha design permits the conversion to take place directly in bothdirections, i.e. up/down-clockwise/counter-clockwise. This is becausethe cable is wound onto or off the turning body. It will be understoodthat the windable component may naturally be of some other type such asa wire, chain, tape or the line.

In accordance with a further embodiment the turning body and the rotorare arranged on a common, substantially horizontal shaft.

Since these two components are arranged on a common shaft the rotarymovement is transmitted substantially without losses and the horizontalorientation of the shaft enables easy conversion of the verticalmovement of the floating body to the rotary movement of the turningbody.

In accordance with yet another preferred embodiment the turning body hascircular cross section and the diameter of the rotor is larger than thatof the turning body. It is particularly advantageous for the diameter ofthe rotor to be several times greater than that of the turning body.

Thanks to the rotor having a larger diameter than that of the turningbody, the peripheral speed is increased without the need for any specialextra gear mechanism since the difference in diameter per se constitutesthe gear mechanism. Since the linear movement of the floating body takesplace at moderate speed, in the order of 0.5–0.8 m/s, an increase isdesirable in order to increase the frequency of the induced voltage.

In accordance with another preferred embodiment the movementtransmitting means is secured by its upper end to the floating body andby its lower end to the rotor, at least the lower part of the movementtransmitting means consisting of a component that can be rolled up, suchas a cable or the like.

The movement transmitting means can thus be attached directly to therotor, which may be a practical solution if the rotor is arrangedoutside the stator. The construction will thus be very simple and have aminimum number of movable parts.

In accordance with yet another preferred embodiment spring means isarranged to exert a torsional force on the rotor.

Applying such a spring means allows the movement transmitting means tobe of simple design since it is sufficient for it to be unidirectionaland is only active during upward movement of the floating body. Duringthis movement the spring is stretched and its stored energy is used torotary the rotor during the downward movement of the floating body.

In accordance with a further preferred embodiment the spring rate of thespring means is adjustable.

The spring can thus be adjusted to suit the wave conditions as regardswave height and velocity so that resonance is achieved between themovement of the floating body and the spring. This minimizesdisturbances in the movement and enables current to be induced in auniform and harmonious manner.

In accordance with another preferred embodiment the housing is securedto a base plate arranged to rest on the bed of the sea/lake.

Since the housing is applied on the sea bed the generator will be stableand substantially unaffected by underwater currents. The base plate mayhave relatively large mass, which also increases stability.

In accordance with yet another preferred embodiment the length of themovement transmitting means is adjustable.

This allows, for instance, for adjustment to different levels of thesurface of the sea/lake as in the case of tidal waters.

In accordance with yet another preferred embodiment the housing isfilled with a liquid.

This embodiment is particularly significant if the generator is placedin relatively deep water since the pressure difference would otherwisemake it complicated to efficiently seal the housing. If the housing isfilled with a liquid of a type less aggressive than salt water, the riskis substantially eliminated of it later penetrating, even withcomparatively simple bushings on the housing. The generator is alsocooled by the liquid. The liquid should suitably have the same pressureas the surroundings.

In accordance with yet another preferred embodiment the housing isprimarily made of concrete.

Concrete is the cheapest possible material that could be used in thiscontext. Furthermore, in many cases it is important for the unit to havea high ballast weight and the material costs are then of considerablesignificance.

In accordance with yet another preferred embodiment the floating body isconnected via the movement transmitting means to a plurality ofgenerators.

Such duplication or multiplication on the generator side may in certaincases lead to a totally more economic unit since each generator can bean entirely standard unit and, depending on the locality, a suitablenumber can be connected to one and the same floating body.

In accordance with yet another preferred embodiment the stator windingsare connected to a rectifier. This rectifier is suitably arranged closeto the linear generator below the surface of the water.

In accordance with yet another preferred embodiment the generator isarranged to produce a voltage of varying frequency. This is because,after being rectified, the output signal is a bipolar DC voltage.

The generator is thus suited to the movement pattern created in therotor by the wave movements, the speed varying depending on where in awave cycle the floating body is and on superimposed variations in themovement of the wave surface.

In accordance with yet another preferred embodiment the movementtransmitting means comprises a second gear mechanism to effect a gearchange of the vertical movement of the floating body.

This offers a supplementary or alternative method of increasing thefrequency of the induced voltage.

In accordance with yet another preferred embodiment the unit comprises afree wheel arranged to convert oscillating rotary movement tounidirectional rotary movement.

Admittedly this embodiment introduces yet another component in the unit.However, it instead offers the advantage of simpler stator windingdesign and results in a cleaner profile of the induced voltage.

In accordance with yet another preferred embodiment the stator windingconsists of a cable comprising a current conductor, a firstsemi-conducting layer surrounding the conductor, an insulating layer ofsolid insulation surrounding the first semi-conducting layer, and asecond semi-conducting layer surrounding the insulating layer.

A winding of this type can endure current of extremely high voltagebeing induced. The need of a transformer between the generator and theelectric supply network to which the power is being supplied can thus beeliminated. This is particularly important in the environment in whichthe invention is used.

The advantageous embodiments of the claimed wave-power unit describedabove are defined in the claims subordinate to claim 1.

The claimed wave-power unit is well suited for combination with severalsimilar units to form a wave-power plant. The second aspect of theinvention thus relates to such a power plant wherein the stator windingof each wave-power unit is connected via a rectifier to an inverterwhich is common to a plurality of wave-power units, which inverter isarranged to supply energy to an electric supply network.

The claimed wave-power plant provides a practically realizable solutionfor a system to produce electric current on a larger scale using unitsof the type claimed, thereby exploiting their advantages, and in whichthe conversion to DC and then AC creates favourable transmissionconditions.

In accordance with a preferred embodiment of the claimed wave-powerplant at least one electric switchgear station is connected to thewave-power unit, which switchgear station comprises a watertightcontainer enclosing switchgear components, which container is anchoredin the sea bed.

In order to obtain economic energy production from generator units atsea that utilize wave movement, it is important to effect technicaloptimization not only of the generator unit but also of the completesystem required to transmit the energy from each energy source to anelectric network for transmission and distribution. An important aspecthere is that the wave-power plant is located some distance off shore,which distance is sometimes considerable.

Thanks to its connection to a switchgear station so designed, it can beplaced close to the generator unit. This minimizes losses and enablesthe energy from a plurality of wave-power units to be transferred via asimple common cable connected to the electric supply network on land.This offers a comprehensive solution where both the wave-power unit andthe switchgear station can be constructed as standard modules usingstandard components. Besides being economic in both construction andoperation, a power plant in accordance with the invention also offersadvantages from the environmental aspect since no switchgear buildingsneed be built in environmentally sensitive coastal areas.

In accordance with another preferred embodiment the system comprises aplurality of switchgear stations wherein each is connected to a numberof wave-power units. Such an embodiment may sometimes be advantageous ifthe number of units is large.

In accordance with yet another preferred embodiment each switchgearstation is connected to a receiving station arranged on land.

In accordance with yet another preferred embodiment at least one of theswitchgear stations, normally all of them, comprises a step-uptransformer. Alternatively, or as well, a step-up transformer isarranged in the intermediate station. Transmitting the energy at anincreased voltage level achieves more favourable transmission both fromthe technical and the financial aspect.

In accordance with yet another preferred embodiment the switchgearstations and/or the intermediate station comprise(s) a converter. Thevoltage can thus be favourably transmitted as AC.

In accordance with yet another preferred embodiment the switchgearstations and/or the intermediate station comprise(s) means for storingenergy. The system can then easily adjust the power supplied dependingon fluctuations in available power and power required.

In accordance with yet another preferred embodiment the switchgearstations and/or the intermediate station comprise(s) filtering means forfiltering outgoing and/or incoming current and voltage. The voltagesupplied by generator units of the type in question may in many cases beunstable and may vary as to frequency and amplitude, as well ascontaining heterodyne frequencies. The arrangement of filtering meanseliminates these defects or at least reduces them so that a cleanvoltage, free from disturbance, is transmitted to the network.

In accordance with yet another preferred embodiment the switchgearstations and/or the intermediate station is/are filled with anon-corrosive, buffered liquid. This prevents aggressive salt water frompenetrating, and the components in the switchgear and intermediatestations are protected.

In accordance with yet another preferred embodiment a filter and/or atransformer is/are arranged after the inverter. This ensures that aclean, ideal voltage can be supplied and that it can be conveyed furtherto a transmission or distribution network with suitably stepped-upvoltage.

In accordance with yet another preferred embodiment the filter and/ortransformer is/are arranged on land.

This offers a more suitable solution from the plant and operatingaspects than if these components were to be situated at sea.

In accordance with yet another preferred embodiment each wave-power unitis connected to the inverter via a cable arranged on or close to the seaor lake bed.

Since the cable is arranged close to the sea bed there is less risk thanotherwise of it causing any disruption to the surroundings or beingtampered with.

The advantageous embodiments of the claimed wave-power plant describedabove are defined in the subordinate claims to claim 24.

In a third aspect of the invention the objective set is achieved by theuse of the claimed wave-power unit or the wave-power plant forgenerating electric power, thereby gaining advantages of the typeindicated above.

The objective set is achieved in a fourth aspect of the invention inthat a method of the kind described in the preamble to claim 37comprises the special measures of enclosing at least the stator of thegenerator in a watertight housing, anchoring the housing in the sea/lakebed, and arranging mechanical movement transmitting means to transmitvertical movements of the floating body to rotary movements of thegenerator rotor.

In accordance with a preferred embodiment the claimed method is utilizedwhile making use of the wave-power unit and the preferred embodimentsthereof.

Advantages are thus gained equivalent to those described above for thewave-power unit and its preferred embodiments.

In accordance with another preferred embodiment of the claimed methodthe spring rate is adjusted so that resonance is obtained with themovement of the floating body that is estimated to occur for most of thetime.

In accordance with yet another preferred embodiment the energy generatedis conducted to a switchgear station, the components of which arearranged in a watertight container, which container is anchored in thesea bed.

The preferred embodiments of the claimed method described above aredefined in the subordinate claims to claim 37.

The invention is described in more detail in the following detaileddescription of advantageous examples thereof, with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view from the side of a wave-power unit inaccordance with the invention.

FIG. 2 illustrates the turning body and rotor of a unit in accordancewith the invention.

FIGS. 3 and 4 show alternative embodiments of the turning body.

FIG. 5 is a circuit diagram illustrating how a plurality of units arecombined to form a wave-power plant.

FIG. 5 a shows an alternative rectifying example.

FIG. 6 is a cross section through a cable in the stator winding inaccordance with one embodiment of the invention.

FIG. 7 is a schematic view from the side of a generator in accordancewith an alternative embodiment of the invention.

FIG. 8 shows a view from the side of a component in a unit in accordancewith one embodiment of the invention.

FIG. 9 is a side view of another alternative embodiment of the unit inaccordance with the invention.

FIG. 10 is a diagram illustrating another component of a unit inaccordance with an embodiment of the invention.

FIG. 11 is a diagram illustrating another component.

FIG. 12 illustrates how the wave-power unit forms a wave-power plant andhow it is connected to an electric supply network.

FIG. 13 illustrates a side view of the wave-power unit connected to aswitchgear station.

FIG. 14 illustrates an alternative method of connecting the wave-powerunit to a supply network.

FIGS. 15–18 are charts illustrating various examples of converting thevoltage in a power plant in accordance with the invention.

FIG. 19 illustrates an alternative rectifying example.

DESCRIPTION OF THE INVENTION

FIG. 1 shows a side view of a wave-power unit in accordance with theinvention. A floating body 3 is arranged to float on the surface 2 ofthe ocean. An electric synchronous generator 5 with permanent magnetrotor is anchored via a base plate 8 secured in the sea bed. Thegenerator 5 is arranged in a liquid-tight housing for by the base plate8 and a cover 6. The housing is proof against salt water and watertight.It may possibly be filled with a gas or a liquid. The rotor shaft 9 ofthe generator 5 extends out through a sealed lead-in in one wall of thehousing. A turning body 10 is fixed to the protruding part of the rotorshaft 9. The turning body 10 is in the form of a circular cylinder withconcave envelope surface. The shaft is rotatably supported by a firstbearing 11 arranged at the side of the turning body 10 facing away fromthe housing, and a second bearing 12 and third bearing 13 arranged ateach side of the housing.

A cable 4 is secured by one end to the floating body 3 and by its otherend to the turning body 10. The cable 4 is secured to the turning body10 in such a way that it can be wound onto the body. A cable guide 14 isattached to the housing, through which the cable 4 runs. A spring 15 isarranged to exert a torsional force on the rotor shaft 9 in a firstdirection of rotation. The spring may be a cylindrical helical spring ofthe watch spring type. A spring may also be arranged at the other sideof the generator. The spring rate can be controlled by a control device19. The control device is suitably radio-controlled.

Wave movements at the surface 2 of the ocean impart a to-and-frovertical movement to the floating body 3. When the floating body 3 is ina wave trough, part of the cable will be wound around the turning body10. When the floating body is lifted from this position by wave movementthe cable runs off the turning body 10 so that this is caused to rotatein a direction opposite to that of the spring 15, the latter thereforebeing tightened. This continues until the floating body 3 has reachedthe crest of a wave. During the following downward movement of thefloating body 3 the spring 15 placed under tension by the upwardmovement will turn the turning body in the opposite direction so thatthe cable is wound onto the turning body. A resonance working point canbe obtained by adjusting the spring. The movements of the floating body3 are thus converted to an oscillating rotary movement of the turningbody 10, and thus also of the rotor of the generator 5.

A cable 16 is connected to the stator winding of the generator and, viaa cable lead-in, carries the current outside the housing. Inside thehousing the cable is provided with a circuit breaker or contactor 21 anda diode 22 for rectification. The diode may be controlled by athyristor, IGBT or GTO, for instance, or it may be uncontrolled.

Components for monitoring and control may also be arranged in thehousing.

As shown in FIG. 2, the turning body 10 has a diameter considerably lessthan that of the rotor 17. FIGS. 3 and 4 illustrates a couple ofalternative embodiments of the turning body. In FIG. 3 the turning body10 is provided with end flanges 18 to ensure that the cable does notslip off. In the example shown in FIG. 4 this is achieved by the turningbody 10 being concave as seen in a longitudinal section.

A gear exchange is thus obtained that gives the rotor a peripheral speedwhich is correspondingly greater than the peripheral speed of theturning body. Mechanism for additional step-up may naturally bearranged.

A wave-power plant in accordance with the invention consists of two ormore units of the type described above. FIG. 5 illustrates how these areconnected together to supply energy to an electric supply network. Inthe example shown the power plant consists of three units, symbolicallydesignated 20 a–20 c. Each unit is connected via a breaker or contactor21 and a rectifier 22 to an inverter 23 in a bipolar connectionaccording to the figure. The circuit diagram is only drawn in for theunit 20 a. It will be understood that the other units 20 b, 20 c areconnected in corresponding manner. The inverter 23 supplies three-phasecurrent to the electric supply network 25, possibly via a transformer 24and/or a filter.

The rectifiers may be diodes, which may be controlled and of type IGBT,GTO or thyristors, comprise controlled bipolar components or they maynot be controlled. The voltages on the DC side may be connected inparallel or in series, or a combination of both.

Alternatively a full-wave rectifier of the type illustrated in FIG. 5 amay be used.

FIG. 6 shows a cross section through a high-voltage cable that may beadvantageous to use for the stator winding in certain applications ofthe invention. The cable consists of a core with one or more strandparts 31 of copper. The core is surrounded by an inner semiconductinglayer 32. Outside this is a layer of solid insulation 33, e.g. PEXinsulation. Around the insulation is an outer semiconducting layer 34.Each of the semiconducting layers forms an equipotential surface.

FIG. 7 illustrates schematically, seen from the side, an alternativeembodiment of the generator in a wave-power unit in accordance with theinvention. In this example only the stator is enclosed in the housing 6which may be of concrete. The rotor 17 is thus not enclosed. It islocated outside the stator. Vertical movements of the floating body arehere transmitted directly to the rotor 17 since the cable 4 is attachedto the outside of the rotor. When the floating body (not shown in thisfigure) moves up and down, the cable is wound off and on to the rotor 17so that this performs an oscillating rotary movement. The rotor isjournalled directly on the outside of the housing 6.

FIG. 8 illustrates how the cable 4 is provided with a control devicecontrolling its active length, i.e. the distance between the floatingbody 3 and the generator 6. In this case the control device consists ofa roll 29 secured to the floating body, onto which roll a part of thecable can be wound. The control device may also be designed in someother way or may alternatively be arranged at the connection point ofthe cable to the rotor, or somewhere else along the cable. The controldevice allows the length of the cable to be adjusted to varying tidalwater conditions. It can also be used to position the floating bodyimmediately below the surface of the water. When the connecting means isof some other type than a cable, wire, chain or jointed rods, a controldevice suitable for the particular type shall be used.

FIG. 9 shows an example in which a floating body 3 is common to twoseparate generators 6 a, 6 b. The cable 4 is connected to a horizontalrod 38 which, via cables 4 a, 4 b, is connected to respective generators4 a, 4 b.

FIG. 10 illustrates an embodiment in which the cable is provided with apiston mechanism. In the embodiment shown the piston mechanism consistsof a first piston 30 secured to the upper part 4 d of the cable andarranged to sealingly move up and down in a container 32 filled withliquid, and of a second piston 31 connected to the lower part 4 c of thecable and similarly arranged to move up and down in the container 32.The first piston 30 connected to the cable 4 d and the part of thecontainer 32 cooperating therewith have larger diameter than the secondpiston 31 connected to the cable 4 c and the part of the container 32cooperating with this piston. The position of the container is suitablyfixed. With this arrangement a ratio is obtained between the verticalmovement of the upper cable 4 d and the vertical movement of the lowercable 4 c that corresponds to the area ratio between the pistons. Thepiston mechanism may alternatively be designed as a link system, toothedwheel or using screws of different pitch. The piston mechanism may alsobe designed so that adjustment of the piston ratio is possible.

FIG. 11 illustrates how the turning body 10 is connected to the rotor 17via a free wheel 28. The free wheel 28 is arranged to convert theoscillating rotary movement of the turning body 10 to unidirectionalrotary movement of the rotor 17.

FIG. 12 illustrates a wave-power plant with a plurality of generators 20a, 20 b, 20 c interconnected. A rectifier is arranged at each generatorand, via cables 39 arranged on the sea bed, the DC current is conductedto a station on land with an inverter 23, a transformer 24 and a filter41 from whence the electric power is supplied to a distribution ortransmission network. The transformer may be omitted if a winding of thetype shown in FIG. 6 is used.

FIG. 13 is a basic layout sketch illustrating another advantageousembodiment of the invention. A switchgear station 101 is arrangedresting on the sea bed B. The switchgear station 101 consists of awatertight container formed by a housing 102 and a bottom plate 103which may be of concrete, for instance. The switchgear station 101 isanchored in the sea bed B. The generators 104–109 of a number ofwave-power units are connected to the switchgear station.

Each generator unit 104–109 is electrically connected with theswitchgear station 101 by cables 110–115 which, via lead-ins through thehousing 102, are connected to the components inside the switchgearstation. The voltage is supplied from each unit as low-voltage direct oralternating voltage.

The components in the switchgear station 101 are of conventional typeand are not shown in the figures. These components may includesemiconductors, converters, breakers, measuring devices, relayprotection, surge diverters and other over-voltage protection devices,earthing means, load couplers or disconnectors, as well as transformers.

The switchgear station supplies an outgoing direct or alternatingvoltage, preferably high voltage, through outgoing cables 116. Thealternating voltage has low frequency and may be three phase ormultiphase. Standard frequencies such as 50 or 60 Hz may also be used.

The incoming low voltage is converted to outgoing high voltage by thetransformer in the switchgear station. The converter or inverter in theswitchgear station is used when necessary to converter DC-AC or viceversa.

The voltage is supplied to a receiving station located on land, possiblyvia an intermediate station, to be fed out on an electric supplynetwork.

FIG. 14 illustrates an example of a system in accordance with theinvention that may be expedient when a large number of generator unitsis included in the system. The figure is a symbolic representation ofthe system seen in bird's eye perspective and shows a sea area H on theleft of the figure and a land area L on the right. The components on theleft of the figure are located partly under and partly above the surfaceof the water.

The system comprises a first group of generator units 104 a–106 a, asecond group of generator units 104 b–106 b and a third group ofgenerator units 104 c–106 c. The generator units 104 a–106 a in thefirst group are connected via under-water cables to a first switchgearstation 101 a located below the surface of the water. Similarly, the twoother groups of generators 104 b–106 b and 104 c–106 c are connected toa second switchgear station 101 b and a third switchgear station 101 c,respectively. Each of the switchgear stations 101 a–101 c is connectedvia under-water cables 116 a–116 c to an intermediate station 117, alsolocated below the surface of the water. The voltage is conducted fromthe intermediate station 117 as low-frequency three-phase alternatingvoltage via under-water cables 118 to a receiving station 119 located onland. The voltage is converted in the receiving station to a standardfrequency such as 50 or 60 Hz.

The distance between the generator units and the receiving station maybe from a kilometer or so up to many tens of kilometers. When the systemis constructed as shown in FIG. 14 the distance between on the one handswitchgear station and intermediate station and on the other handintermediate station and receiving station, can be optimized.

Transmission from the generator units to a receiving station on land maytake place in various ways with various voltage conversions. FIGS. 15 to18 illustrate schematically some examples of this. In each example thegenerator units are arranged to the left and the receiving station onland L to the right in the figures. 121 denotes a converter/inverter and122 a step-up transformer. In FIGS. 15 and 16 the generator units supplydirect voltage which in FIG. 15 is transmitted to land as alternatingvoltage and in FIG. 16 as direct voltage.

In FIGS. 17 and 18 the generator units supply alternating voltage whichis converted to direct voltage. In FIG. 17 this is transmitted to landas alternating voltage and in FIG. 18 as direct voltage.

Many other alternatives are shown within the scope of the invention,such as a whole-wave rectifier of the type illustrated in FIG. 19.

Energy stores and filters may also be housed in each switchgear station111 and/or in the intermediate station 117. The energy stores mayconsist of batteries, capacitors, SMES types, flywheels or combinationsthereof, for instance. The filters may comprise active components insimilar manner to the converters. Passive LC filters andelectro-mechanical components such as flywheel converters or synchronouscondensers are also possible.

1. A wave-power unit for the production of electric power comprising:floating body and rotating electric generator having a rotor; amechanical movement transmitting means arranged for transmission ofvertical movement of the floating body to rotary movements of the rotor,a turning body connected to the transmitting means, the transmittingmeans being secured by its upper end to the floating body and by itslower end to the turning body; the lower part of the movementtransmitting means including a component that can be rolled up; theturning body having circular cross section and the diameter of the rotoris larger than the turning body.
 2. A wave-power unit as claimed inclaim 1, wherein at least the stator of the generator is enclosed in ahousing anchored in the sea/lake bed.
 3. A wave-power unit as claimed inclaim 2, wherein the rotor is also enclosed in the housing.
 4. Awave-power unit as claimed in claim 1, wherein the rotor is situated onthe outside of the stator.
 5. A wave-power unit as claimed in claim 1,wherein the turning body is arranged outside the housing.
 6. Awave-power unit as claimed in claim 1, comprising a first gear mechanismeffecting a gear change between the movements of the turning body andthe rotor.
 7. A wave-power unit as claimed in claim 1, wherein theturning body and the rotor are arranged on a common, substantiallyhorizontal shaft.
 8. A wave-power unit as claimed in claim 1, wherein itis provided with spring means arranged to exert a torsional force on therotor.
 9. A wave-power unit as claimed in claim 8, wherein the springrate of the spring means is adjustable.
 10. A wave-power unit as claimedin claim 1, wherein the housing which base plate is arranged to rest onthe bed of the sea/lake.
 11. A wave-power unit as claimed in claim 1,wherein the length of the movement transmitting means is adjustable. 12.A wave-power unit as claimed in claim 1, wherein the housing is filledwith a liquid.
 13. A wave-power unit as claimed in claim 1, wherein thehousing is primarily made of concrete.
 14. A wave-power unit as claimedin claim 1, wherein the floating body is connected to a plurality ofgenerators.
 15. A wave-power unit as claimed in claim 1, wherein thestator winding is connected to a rectifier, which rectifier ispreferably arranged close to the generator below the surface of thewater, preferably inside the housing.
 16. A wave-power unit as claimedin claim 1, wherein the generator is arranged to produce a voltage ofvarying frequency.
 17. A wave-power unit as claimed in claim 1, whereinthe movement transmitting means comprises a piston mechanism to effect agear ratio of the vertical movement of the floating body.
 18. Awave-power unit as claimed in claim 1, wherein it comprises a free wheelarranged to convert oscillating rotary movement to unidirectional rotarymovement.
 19. A wave-power unit as claimed in claim 1, wherein thestator winding consists of a cable comprising a current conductor, afirst semi-conducting layer surrounding the conductor, an insulatinglayer of solid insulation surrounding the first semi-conducting layer,and a second semi-conducting layer surrounding the insulating layer. 20.A wave-power plant comprising a plurality of wave-power units as claimedin claim 1, wherein the stator winding of each wave-power unit isconnected via a rectifier to an inverter which is common to a pluralityof wave-power units, which inverter is arranged to supply energy to anelectric supply network.
 21. A wave-power plant as claimed in claim 20,wherein at least one electric switchgear station is connected to thewave-power unit, which switchgear station comprises a watertightcontainer housing switchgear components, which container is anchored inthe sea bed.
 22. A wave-power plant as claimed in claim 21, wherein aplurality of switchgear stations are connected to the wave-power unit,each switchgear station being connected to a number of wave-power units.23. A wave-power plant as claimed in claim 21, wherein each switchgearstation is connected to a receiving station arranged on land.
 24. Awave-power plant as claimed in claim 21, wherein at least one of theswitchgear stations comprises a step-up transformer and/or anintermediate station comprising a step-up transformer.
 25. A wave-powerplant as claimed in claim 21, wherein at least one of the switchgearstations and/or the intermediate station comprises a converter.
 26. Awave-power plant as claimed in claim 25, wherein at least one of theswitchgear stations and/or the intermediate station comprises filteringmeans for filtering outgoing and/or incoming current and voltage.
 27. Awave-power plant as claimed in claim 21, wherein at least one of theswitchgear stations and/or the intermediate station comprises means forstoring energy.
 28. A wave-power plant as claimed claim 21, wherein atleast one of the switchgear stations and/or the intermediate station isfilled with non-corrosive, buffered liquid.
 29. A wave-power plant asclaimed in claim 20, wherein a filter and/or a transformer is/arearranged after the inverter.
 30. A wave-power plant as claimed in claim20, wherein the inverter, filter and/or transformer is/are arranged onland.
 31. A wave-power plant as claimed in claim 20, wherein eachwave-power unit is connected to the inverter via a cable arranged on orclose to the sea or lake bed.
 32. A method of generating electric powerby mechanically connecting a floating body to a rotating electricgenerator, wherein mechanical movement transmitting means is arranged totransmit vertical movements of the floating body to rotary movements ofthe generator rotor, the rotor being connected to a turning bodyconnected to the movement transmitting means, said movement transmittingmeans being secured by its upper end to the floating body and by itslower end to the turning body, and at least the lower part of themovement transmitting means includes a component that can be rolled up,wherein the turning body has circular cross section and the diameter ofthe rotor is larger than the turning body.
 33. A method as claimed inclaim 32, wherein the method is utilized while making use of awave-power unit.
 34. A method as claimed in claim 33, wherein the springmeans with adjustable spring rate is applied to exert a torsional forceon the rotor and in that the spring means is adjusted so that resonanceis obtained with the movement of the floating body that is estimated tooccur for most of the time.
 35. A method as claimed in claim 32, whereinthe energy generated is conducted to a switchgear station, thecomponents of which are arranged in a watertight container, whichcontainer is anchored in the sea bed.
 36. A method as claimed in claim35, wherein the switchgear station is connected to a receiving stationarranged on land.
 37. A method as claimed in claim 36, wherein aplurality of switchgear stations are connected to a common intermediatestation, which intermediate station is connected to the receivingstation.
 38. A method as claimed in claim 35, wherein at least one ofthe switchgear stations and/or the receiving station is/are arrangedbelow the surface of the water, preferably close to the sea bed.
 39. Amethod as claimed in claim 35, wherein voltage generated is step-uptransformed in at least one of the switchgear stations and/or theintermediate station.
 40. A method as claimed in claim 35, wherein theoutgoing voltage from at least one of the switchgear stations and/orfrom the intermediate station is alternating voltage.
 41. A wave-powerunit for the production of electric power comprising: floating body androtating electric generator having a rotor; a mechanical movementtransmitting means arranged for transmission of vertical movement of thefloating body to rotary movements of the rotor, a turning body connectedto the transmitting means, the transmitting means being secured by itsupper end to the floating body and by its lower end to the turning body;the lower part of the movement transmitting means including a componentthat can be rolled up; wherein the spring rate of the spring means isadjustable.
 42. A wave-power unit for the production of electric powercomprising: a floating body and rotating electric generator having arotor; a mechanical movement transmitting means arranged fortransmission of vertical movement of the floating body to rotarymovements of the rotor, a turning body connected to the transmittingmeans, the transmitting means being secured by its upper end to thefloating body and by its lower end to the turning body; the lower partof the movement transmitting means including a component that can berolled up; wherein at least a stator of the generator is enclosed in ahousing anchored in the sea/lake bed and wherein the housing is filledwith a liquid.